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Fossil snails explain ancient transition

April 22, 2013 in Science

EMBARGOED until 1900 GMT on 22 April

Fossilised snail shells shed light on the transition from warmth to deep cold Image: Jim Conrad

Fossil snails shed light on the transition from warmth to deep cold
Image: Jim Conrad

By Tim Radford

The fossilised remains of snails are helping scientists to understand how a fall in carbon dioxide levels signalled the start of a far colder and quite different climate.

LONDON, 22 April – British and American scientists have used a new technique to pinpoint an epoch-making moment of climate change.

They have used isotopes from land snails in what is now Hampshire and the Isle of Wight in England to reconstruct a fateful fall in carbon dioxide levels in the atmosphere, when average air temperatures fell by up to 6°C, summer freshwater temperatures plummeted 10°C and great sheets of ice began to form.

Almost 34 million years ago, the late Eocene epoch gave way to the Oligocene. In a much warmer world, carbon dioxide levels in the atmosphere had reached 1,000 parts per million (ppm), and then started to fall precipitately.

Within about 400,000 years huge glaciers dominated the polar regions, sea levels fell, faunas were extinguished and the world had changed forever.

Palaeontologists, climate scientists and geophysicists have repeatedly tried to reconstruct the sequence of events that turned a hot, marshy world into a freezing one, but any physical evidence of ancient planetary catastrophe has been buried, or eroded, or washed away.

Marine sediments have preserved the temperature conditions as they changed. Changes in the fossil sequence tell a story of extinctions in Europe and the migration of new genera from Asia. But like most of the great extinctions from the past – and this was a relatively minor period of mass extinction – the cause remains a mystery.

“By understanding past climate transitions, we can better understand the present and predict impacts for the future”

But isotope evidence from fossil shells of the snail Viviparius lentus seems to have settled one point: the dramatic shift is firmly linked to changes in carbon dioxide levels in the atmosphere.

Michael Hren of the University of Connecticut and colleagues report in the Proceedings of the National Academy of Sciences that heavy isotopes of carbon and oxygen in snail fossils could be interpreted to serve as records of temperatures at the time the shells formed.

The past, too, has lessons for the future. Carbon dioxide levels in the atmosphere, thanks to the burning of fossil fuels, are rising again: nearly 400 ppm now and in danger of increasing once again to 1,000 ppm in the next 100 years.

If a sharp drop in temperature fundamentally altered life on Earth 34 million years ago, another, even swifter rise in atmospheric and fresh water temperatures during the next century would do the same.

“One of the key principles of geology is that the past is the key to the present: records of past climate inform us of how the Earth system functions”, said Dr Hren. “By understanding past climate transitions, we can better understand the present and predict impacts for the future.” – Climate News Network

Why we should be cooling, not warming

March 7, 2013 in Warming

EMBARGOED until 1900 GMT on Thursday 7 March

Evidence from tree rings may be disputed: This study looked more widely Image: Arnoldius

Evidence from tree rings may be disputed: This study looked more widely
Image: Arnoldius

By Tim Radford

Reconstructing the climate over the last 11,000 years shows that the Earth was once warmer than it is now – but that it would still be cooling today without the influence of greenhouse gases.

LONDON, 7 March – US scientists have checked climate history for the past 11,300 years and come to one comforting conclusion. It has been warmer in human history, but those long hot summers happened long before the invention of cities, empires and scribes to record them.

But soon all records will be broken: by 2100, when global temperatures will be higher than at any point since the end of the last Ice Age, according to a study in the journal Science (see EurekAlert! for the release).

Shaun Marcott and colleagues from Oregon State University and Harvard University decided to look once again at the big picture.

They examined reconstructions of past climates from fossil data, along with isotopes from terrestrial and marine sediments, from 73 sites around the globe, and tried to assess the main trends of climate change from the beginning of the Holocene – the geologists’ label for the epoch in which we now live.

They chose to go as far back as possible in time across a wide range of locations, because there are always arguments about the reliability of readings from, say, tree rings, or indirect evidence from European monastic or naval records in the past 1500 years.

These suggest an unprecedented warming, but the researchers felt that a clearer picture should emerge over a longer timespan.

Only one explanation


“When you look at just one part of the world, the temperature history can be affected by regional climate variations. But when you combine the sites from all around the world, you can average out those regional anomalies and get a clear sense of the Earth’s global temperature history”, said Peter Clark, a co-author.

They found that, for the first 5,000 years after the end of the Ice Age, the world warmed by about 0.6°C. Then from about 5,500 years before the present to just 100 years ago, there was a slow cooling of about 0.7°C, reaching a low point during the so-called Little Ice Age, when Londoners held “frost fairs” on the frozen Thames.

This cooling, the researchers say, is linked to a 2°C temperature change in the North Atlantic. Such changes were almost certainly linked to cycles in the Earth’s orbit and to changes in the planet’s orientation that affect the levels of sunlight hitting the northern hemisphere.

“As the Earth’s orientation changed, northern hemisphere summers became cooler, and we should almost be near the bottom of a long-term cooling trend – but obviously, we are not”, said Dr Marcott.

The world should, in other words, still be in a cool phase. But in the last century, global temperatures have increased rapidly: from very nearly the coldest to the warmest levels of the Holocene. The only variable that can explain the rise is the rapid increase in carbon dioxide emissions due to human activity (see our story of 6 March, Coal triggers carbon level rise).

And although the world is now warmer than it has been for most – but not all – of the last 11,300 years, by 2100, according to virtually every climate model, average global temperatures will be higher than at any time since the end of the Ice Age. – Climate News Network

Brazil’s stunted generation

February 4, 2013 in Development Issues

EMBARGOED till 0001 GMT on Monday 4 February

The result of a starvation diet - Brazil 30 years ago

The result of a starvation diet – Brazil 30 years ago

By Jan Rocha

The fossil record suggests that one response to a warmer world is for many species to become smaller as nutritious food becomes scarcer. Within living memory this became a tragic reality in Brazil.

SAO PAULO, 4 February – The prediction by scientists that humans would respond to climate change by becoming hobbit-sized in order to survive has already happened in Brazil. A near-starving population in the north-east of the country produced a generation of children who became pigmy-sized adults after being brought up on a diet of rats, snakes and cacti. Adults grew to only 1.35 metres (4ft 6ins).

This is exactly what scientists had predicted. They were looking at the fossil record of the last time the world had warmed by 6°C, 55 million years ago. In a warmer world, the 30 scientists concluded, plants became less nutritious and mammals, insects and even earthworms had to eat more to survive. In response they became smaller and reproduced earlier.

The Climate News Network reported exclusively on the work of the Bighorn Basin Coring Project, involving scientists from the US, UK, Germany, and the Netherlands, on 7 January. Dr Phillip Jardine, from the Department of Geography at Birmingham University, said that dwarfism was expected to be a successful survival strategy.

Unknown to the scientists on the project, this apocalyptic vision of the future had, in fact, already occurred. In the 1980s Brazil’s Northeast, the poorest, most backward region of the country, much of it semi-arid, was hit by a prolonged drought that left millions of families starving. Without food, they resorted to eating rodents and cactus plants.

They were encouraged by a local Red Cross doctor, José Pontes Neto, who said: “Go on eating rats, snakes and chameleons, they are a source of protein.” But the doctor warned that the infant population in the drought areas was so riddled with intestinal worms and chronic hunger that the result would be a generation of “nanicos” – dwarfs.

His comments were published in a UNICEF study carried out at the time. It concluded that three and a half million children aged one to five years old were permanently affected by dwarfism. Specialists called it “nutritional dwarfism”.

Man-made hunger to blame


One of Brazil’s leading researchers into nutrition at the time, Dr Nelson Chaves, blamed the region’s chronic sub-nutrition not only on the long-lasting drought, but on the existing unequal social structures.

In a report published in April 1984, entitled Northeast: Drought, Hunger and Misery, carried out by IBASE, the Brazilian Institute for Social and Economic Analyses, a well-respected NGO, he wrote:

“Due to protein deficiency, the stature of the population in Zona da Mata (the main sugarcane growing region) is progressively diminishing, becoming similar to that of African pigmies.

“But the dwarfism of the African pigmy is genetic, while the march towards dwarfism we see here is from sub-nutrition. It is a consequence of progressive endemic hunger, caused and maintained by man. It is hunger resulting from economic and social inequality, from poverty… The final result is a deteriorated population, sick, hungry”.

Dr Chaves said that while the sugarcane plantations, owned by the local elite, received financial support from the then military government, impoverished rural workers were ignored.

At the time, the workers were not even allowed to keep vegetable plots for their own subsistence, because every inch of land had to be used for sugarcane. Underpaid and exploited, people could afford to buy little food. Their basic diet, consisting of beans and manioc flour, lacked protein. Meat was almost never eaten.

Seven years later, on 19 November 1991, the Brazilian newspaper A Folha de São Paulo caused a sensation with a front-page story entitled Gabiru man is a new species in the Northeast.

Reporter Xico Sa wrote: “A new sub-race is appearing in Brazil, made up of tiny people. They are the same size as African pigmies and they have been baptised gabiru men. This ‘sub-race’ is the result of hunger, subnutrition and poverty’.”

Life-long consequences


Gabiru is the name of a species of large rat found in the region, and was originally given to the undersized inhabitants by Brazilian sociologist Josue de Castro, in his classic study The Geography of Hunger.

The newspaper story was illustrated with photographs of a so-called gabiru-man, Amauro Silva, just 1.35 cm high.

As a result of the Folha’s story, a parliamentary committee of inquiry was set up to enquire into the causes of hunger in Brazil. It concluded that six million children were undernourished and that 10% of them would suffer the consequences for the rest of their lives.

Since the 1980s nutritional standards in the Northeast region have improved along with the economic situation. Between 1989 and 1997, children’s average height increased by 7 cm, according to research by the government statistics agency, IBGE.

An IBGE researcher said: “Height is one of the best indicators of the quality of life of a population. In the Northeast, logically there are still undernourished and undersized people, but the gabiru is more and more of an exception”.

Since 2002 the introduction of government welfare programmes and increases in the minimum wage have raised millions above the poverty line. IBGE research now shows there are more obese than undernourished people in the region.

These programmes mean that although once again the Northeast is in the grip of a devastating drought, people do not starve. Television coverage shows dried-up riverbeds, withered crops and the carcases of animals that have died of starvation. Water tankers crisscross the dry countryside supplying villages, but people are no longer forced to eat rats and snakes to survive.

The drought cycle in Brazil’s Northeast has existed as long as records go back, but in recent years the droughts have become more frequent. An increase in global warming could make the semi-arid region uninhabitable. – Climate News Network

Mass extinction forecast with 6C temperature rise

January 7, 2013 in Science

EMBARGOED – Not for publication before 0001 GMT on Monday 7 January

By Paul Brown

Hobbit-sized humans, able to exist on less nourishing food, will have the best chance of survival in a warmer world, scientists say.

LONDON, 7 January – Animals, including humans, will shrink in size to survive in a warming world, according to scientists studying the last time the planet’s temperature rose rapidly by 6°C. What scientists call dwarfism was the successful strategy to avoid starvation for a large range of species including horses, many insects and even earthworms. The widespread response was partly to do with the heat but mostly because many plants became less nutritious, forcing mammals and insects to eat far more to survive.

In the next 100 years the combination of more carbon dioxide in the atmosphere and increased temperature could be “catastrophic” for an overpopulated world, according to one of the scientists involved. With food supply drastically reduced, evolutionary forces suggest hobbit-sized humans who needed to eat less would have the greatest chance of survival. These findings are the work of an international group of 30 scientists looking at the vast fossil deposits in rock strata in Wyoming in the US, charting the period 55 million years ago when the Earth’s temperature rose suddenly – as it is expected to do this century.

On that occasion it took 10,000 years for the temperature to rise by 6°C. There were mass extinctions, but the timescale gave some plants and animals time to adapt and move north and south to survive. Many species evolved quickly – dwarfism being one of the most widespread and successful strategies.

The project, entitled the Bighorn Basin Coring Project, involves scientists from the US, the UK, Germany and the Netherlands. It is a United States National Science Foundation-funded project, aimed at understanding what happened the last time the Earth warmed and the consequences for the planet this century. The scientists leading the project are Will Clyde (University of New Hampshire), Philip Gingerich (University of Michigan) and Scott Wing (Smithsonian Institution).

What worries the scientists is that this current warming period will take as little as 200 years, if the Intergovernmental Panel on Climate Change  is correct. This gives many long-lived species, for example trees, no time to evolve and migrate. Even mammals will struggle to move to new areas, because man has placed farmland and cities in the way.

Rapid warming leaves few choices

The result will be mass extinction, and for the survivors, humans, animals and insects, there will be a scramble to eat a diminishing and less nutritious food supply. Lower plant nutrition is caused by higher atmospheric carbon dioxide concentrations, rather than temperature itself. Plant growth experiments have shown that concentrations of both nitrogen and the protein Rubisco, which regulates carbon dioxide fixation, decrease under higher CO2 conditions, making many plant tissues less nutritious.

To get the same calories herbivores would have to eat more plant matter.  Humans would be forced to grow more crops to get the same nutrition from food and spend more time eating it. Farm animals would also get smaller in response, making meat more difficult to obtain. Competition from insects eating food crops would be fierce.

Dwarfism is again expected to be a successful strategy for the survivors, enabling humans, animals and insects to mature earlier with less food and so reproduce before they starve. The researchers’ findings show that earlier optimism that increased carbon dioxide in the atmosphere would have a fertilization effect, allowing food plants to grow quicker in a warmer world, is more than countered by a loss in nutrition. For an overcrowded world this could be disastrous.

Dr Phillip Jardine, one of the scientists involved, is a research fellow at the School of Geography, Earth and Environmental Sciences at Birmingham University, UK. Giving a lecture at the Geological Society of London he said this period of warming, known as the Paleocene-Eocene Thermal Maximum, led to catastrophic extinctions of life in the deep oceans, partly because of increased acidification and partly through lack of oxygen. On land many plants and animals also died out.

“…the impacts of this on a large and growing human population could be catastrophic…”

However, because the warming took place over 10,000 years, many plants and insects were able to adapt, migrating north to avoid the heat or evolving to new forms. Alligators, unimpeded by dams, were able to migrate using natural waterways and lived successfully in the Arctic Circle. In the tropics numerous new species emerged. On the Gulf Coast of America, for example, 20% of species died out but were replaced by others moving in from elsewhere.

Afterwards Dr Jardine was asked by the Climate News Network what effect a 6°C increase would have on the planet currently if not enough action to curb emissions is taken. “For me this just shows how pervasive the impacts of altering the global carbon balance really are”, he said. “Even if future climate change isn’t a convincing enough argument to decrease carbon emissions, increasing atmospheric CO2 concentrations has a very real possibility of reducing the viability of our own food supplies, by compromising the base of the food chain for ourselves and the animals that we farm and eat.

“If we acknowledge the presence of increasing temperatures then we have an additional factor that we would expect to decrease further the size of our farmed animals, and thus the amount of food that we can take from them. I would say that the impacts of this on a large and growing human population could be catastrophic, especially in the developing world and when changes in other resources, for example water, are factored in as well.” - Climate News Network

Read Scott Wing of the Smithsonian Institution